A plurality of fins made of a thin metal sheet are provided on outer surfaces of tubes which are members constituting a heat exchanger such as a radiator for an automobile or a motorcycle, a condenser or an evaporator for a cooler; in order to increase a radiating surface area of the tubes. An aluminum alloy sheet is used in many cases as the material for the above-mentioned tubes because of the light weight and excellent thermal conductivity and corrosion resistance, and in such a case, it is the usual practice to use, as a fin material, a thin Al-Mn aluminum alloy sheet, or a thin Al-Mn alloy clad sheet which is manufactured by applying a film of a brazing metal comprising an Al-Si aluminum alloy onto at least one surface of a thin Al-Mn aluminum alloy sheet as a substrate sheet.
Various methods are available for installing fins made of any of the above-mentioned aluminum alloy sheets on the outer surface of a tube made of an aluminum alloy sheet. Among such various methods, there is widely adopted in the industry a brazing method for brazing at a time many joints between the outer surface of a tube and a plurality of fins, which comprises: provisionally tacking a plurality of fins substantially vertically at prescribed intervals onto the outer surface of a tube by means of an appropriate jig to form an assembly, the outer surface of said tube or at least one surface of each of said plurality of fins being previously applied with a brazing metal film; heating the thus formed assembly to a temperature of from about 580.degree. to about 620.degree. C. in a vacuum furnace or in a furnace filled with an inert gas, or heating the thus formed assembly, many joints of which are covered with a flux, to a temperature of from about 580.degree. to about 620.degree. C. in a furnace filled with air or an inert gas, to melt said brazing metal film; thereby brazing said plurality of fins to the outer surface of said tube with said melted brazing metal at a time by a single heating.
When installing the plurality of fins onto the outer surface of the tube by the above-mentioned method, the following problems are caused: the structure of the aluminum alloy sheet forming the fins is changed under the effect of the heating for brazing, and fine recrystallization grains are produced in the structure of the aluminum alloy sheet. Therefore, when the fins are made of the above-mentioned aluminum alloy clad sheet, the brazing metal melted by the above-mentioned heating penetrates into the gaps among the fine recrystallization grains of the aluminum alloy sheet as the substrate sheet, resulting in a decrease in high-temperature sagging resistance of the fins and, as a result, the fins sag down and deform under the effect of their own weight and cannot hold their original shape upon forming the assembly.
There have been proposed the following aluminum alloy sheets, which are adapted to be used as a fin material for tubes of a heat exchanger, in order to solve the above-mentioned problems:
(1) An aluminum alloy as a fin material, as disclosed in Japanese Patent Provisional Publication No. 57-169,054 dated Oct. 18, 1982, which consists essentially of:
(hereinafter referred to as the "prior art 1").
(2) An aluminum alloy as a fin material, as disclosed in Japanese Patent Provisional Publication No. 58-64,339 dated Apr. 16, 1983, which consists essentially of:
The above-mentioned aluminum alloy may also additionally contain manganese within the range of from 0.1 to 0.9 wt.% and at least one element selected from the group consisting of:
(hereinafter referred to as the "prior art 2").
(3) An aluminum alloy as a fin material, as disclosed in Japanese Patent Provisional Publication No. 59-85,837 dated May 17, 1984, which consists essentially of:
copper: from 0.05 to 0.50 wt.%, and PA1 magnesium: from 0.05 to 0.50 wt.%, PA1 nickel: from 0.05 to 0.30 wt.%, and PA1 iron: from 0.2 to 0.7 wt.%, and PA1 copper: from 0.05 to 0.60 wt.%, and PA1 magnesium: from 0.05 to 0.60 wt.%, where, the total amount of said copper and said magnesium being up to 1.0 wt.%, and PA1 copper: from 0.05 to 0.60 wt.%, and PA1 magnesium: from 0.05 to 0.60 wt.%, where, the total amount of said copper and said magnesium being up to 1.0 wt.%, and
The above-mentioned aluminum alloy may also additionally contain chromium within the range of from 0.05 to 0.30 wt.%.
(hereinafter referred to as the "prior art 3")
(4) A method for manufacturing a fin material from an aluminum alloy, as disclosed in Japanese Patent Provisional Publication No. 60-33,346 dated Feb. 20, 1985, wherein said aluminum alloy consists essentially of:
The above-mentioned aluminum alloy may also additionally contain zirconium within the range of from 0.01 to 0.20 wt.% and/or at least one element selected from the group consisting of:
(hereinafter referred to as the "prior art 4").
(5) An aluminum alloy clad sheet as a fin material, as disclosed in the U.S. Pat. No. 4,511,632 dated Apr. 16, 1985, which consists essentially of:
The above-mentioned aluminum alloy clad sheet may also additionally contain chromium within the range of from 0.05 to 0.40 wt.% and/or at least one element selected from the group consisting of:
(hereinafter referred to as the "prior art 5").
The above-mentioned prior art 1 has the following problems: the high manganese content and the absence of an element for improving sacrificial anode property make an electric potential of the fins noble, resulting in a deteriorated sacrificial anode property of the fins and acceleration of corrosion of the tube. In addition, the absence of an element for improving strength leads to a low room-temperature strength of the fins brazed onto the tube, and deformation of the fins may easily occur under the effect of a wind pressure during service, thus resulting in performance degradation of the heat exchanger. Particularly, because of the recent tendency toward decreasing the thickness of the fins with a view to achieving a smaller weight of the heat exchangers, the above-mentioned sagging down and deformation of the fins are more liable to occur.
The above-mentioned prior art 2 has the following problems: because of the low manganese content, room-temperature strength and high-temperature sagging resistance of the fins brazed onto the tube are both insufficient in spite of the presence of an element for improving strength, leading to easy occurrence of sagging down and deformation of the fins.
The above-mentioned prior art 3 has the following problems: the high manganese content and the absence of an element for improving sacrificial anode property make an electric potential of the fins noble, resulting in a deteriorated sacrificial anode property of the fins and acceleration of corrosion of the tube.
The above-mentioned prior art 4 has the following problems: the absence of an element for improving strength leads to a low room-temperature strength of the fins brazed onto the tube, and deformation of the fins may easily occur under the effect of a wind pressure during service.
The above-mentioned prior art 5 has the following problems: because of the low manganese content, room-temperature strength and high-temperature sagging resistance of the fins brazed onto the tube are both insufficient in spite of the presence of an element for improving strength, leading to easy occurrence of sagging down and deformation of the fins. In addition, the absence of an element for improving sacrificial anode property leads to an insufficient sacrificial anode property in spite of the low manganese content, and corrosion may sometimes occur in the tube.
Under such circumstances, there is a strong demand for the development of an aluminum alloy sheet, which is adapted to be used as a fin material for tubes of a heat exchanger, excellent in high-temperature sagging resistance and sacrificial anode property and having a high room-temperature strength, but an aluminum alloy sheet having such properties has not as yet been proposed.